1. Technical Field
This invention relates generally to battery chargers, and more specifically to smart chargers having capabilities to identify batteries and to charge them accordingly.
2. Background Art
Portable devices routinely depend upon batteries as a power source. To reduce battery replacement costs, rechargeable batteries have found wide utility in powering contemporary consumer and business products. For example, both nickel- and lithium-based batteries may be repeatedly used to energize computers, radios, pagers, phones and other such devices.
Manufacturers have developed many devices for charging batteries. Some of these chargers are in the form of desk-top stands, where the user can leave the stand plugged in all the time and charge the battery simply by placing the device in the stand. The stand thus serves a dual function: first it acts as a charger, and second it acts as a mechanical holder for the electronic device. A problem with chargers of this type is that they can overcharge batteries, thereby compromising battery performance and cycle life.
For example, imagine a person with a two-way radio sitting in a desk-stand charger. If the person wants to transmit a message, he takes the radio out of the stand, presses the xe2x80x9ctalkxe2x80x9d button and sends his message. Once he has finished transmitting, a process that may take a matter of seconds, the person will typically reinsert the radio back into the stand. After all, if the person doesn""t want the radio lying about haphazardly on the desk, the stand provides a tidy and stable holder for the radio.
The problem with this xe2x80x9ctake out; use for a short time; reinsertxe2x80x9d method is that nickel-based batteries can be overcharged. Typical nickel-based battery chargers have at least two modes: rapid charge and trickle charge. When a dead battery is inserted into a charger, the charger wants to charge the battery as fast as possible, so the charger blasts the battery with a high current. This is known as rapid charge. Once the battery xe2x80x9cfills upxe2x80x9d, the charger detects a rapid rise in temperaturexe2x80x94due to cell impedance increasingxe2x80x94and the charger switches to a very low current. The low current, which is just enough to keep the battery topped off, is known as xe2x80x9ctricklexe2x80x9d charge.
When a person takes a fully charged battery out of the charger and uses it for a brief period of time and reinserts it into the charger, the charger has no way of knowing that the battery is nearly fully charged. As a result, the charger blasts the battery in rapid charge mode until it detects a temperature rise. As there is a time delay with the temperature rise, the battery gets ever so slightly over charged. When the process is repeated numerous times, battery reliability is compromised.
Prior art solutions have attempted to solve this problem. For example, U.S. Pat. No. 5,175,211, issued to Brotto, teaches a means of identifying a battery via a resistor identifier or a microprocessor. The problem with the prior art is that it merely identifies the battery type, e.g. xe2x80x9cThis is a lithium batteryxe2x80x9d; or xe2x80x9cThis is a 1 Amp-hour, prismatic, Sony, cell.xe2x80x9d The prior art solutions do not identify the status of charge to avoid overcharging.
There is thus a need for an improved battery identification system.